1,720,971 research outputs found
Ab initio study of CO adsorption on Ni(110): Effects on surface magnetism at low coverage
No full textThe magnetization of the Ni(110) surface is explored as a function of the CO coverage by means of periodic slab calculations within density-functional theory. The in-plane inspection of the spin density corresponding to the surface layer exhibits a CO-induced decrease in the Ni-atom magnetic moments that is limited to the atoms directly involved in the chemisorption bond. This decrease is due to interactions between the metal states and the CO orbitals that increase the population of the spin-down metal states within the outermost layer and decrease that of the corresponding spin-up ones
Adsorption geometry of benzene on Pd(110): Results of first-principles calculations
No full textThe atomic structure of the Pd(110)-c(4 x 2)-benzene system has been determined by means of ab initio slab calculations. A C-2 low-symmetry equilibrium configuration is predicted. The corresponding azimuthal angle theta similar to 11 degrees of the adsorbed molecule is partly due to lateral interactions. The aromatic ring looses planar geometry and the C-H, bonds bend away from the metal. STM images calculated for the C-2 configuration are compatible with recent experimental data
Phonon dispersions: Performance of the generalized gradient approximation
No full textBy computing the phonon dispersions of a few selected solids (Si, C, Al, and Cu), within density-functional perturbation theory, we compare the performance of the local density approximation (LDA) with that of the generalized gradient approximations (GGA's) in the form recently proposed by Perdew, Burke, and Ernzerhof [Phys. Rev. Lett. 77, 3865 (1996)]. We find that GGA systematically lowers the frequencies of phonon branches with positive Gruneisen parameters. This effect is correlated with the GGA's expansion of the lattice constant, since GGA phonon frequencies computed at the experimental lattice constants are higher than the corresponding LDA ones. In C, Al, and Cu, LDA and GGA phonon dispersions have similar accuracy with respect to the experimental data. Si is an exception since the LDA phonon dispersions are already in very good agreement with experiment and GGA worsens the comparison. [S0163-1829(99)03339-1]
CO adsorbed on Cu(001): A comparison between local density approximation and Perdew, Burke, and Ernezerhof generalized gradient approximation
No full textAdsorption energetics, structural and vibrational properties of the Cu(001)-c(2 X 2)-CO system are studied with periodic slab calculations within density functional theory in the local density (LDA) and generalized gradient (GGA) approximations by using ultrasoft pseudopotentials. The recent expression of Perdew, Burke, and Ernzerhof (PBE) has been used as the GGA functional [Phys. Rev; Lett. 77, 3865 (1996)]. The fully relaxed geometry of the system is determined for different adsorption sites,of the CO molecule; unlike LDA, PBE-GGA predicts correctly the on-top adsorption site of the molecule. C-O and Cu-CO bond lengths, stretching frequencies, Cu-layer displacements, chemisorption energies, and work functions are computed under both approximations and are compared to the experimental values. LDA. gives accurate,values for the C-O equilibrium distance and the corresponding stretching frequency, while PBE-GGA better describes the adsorption bond and all the remaining properties. (C) 2001 American Institute of Physics
Interface states at ZnSe/Ge heterojunctions: the role of atomic interdiffusion and disorder
No full textThe origin of electronic states localized at ZnSe/Ge 110 interface is investigated by means of ab initio pseudopotential calculations. Some selected interface configurations are considered, one corresponding to the abrupt interface and others corresponding to partially disordered interfaces, with Zn-Ge or Se-Ge swaps. Remarkably, the existence of interface electronic states within the heterojunction band gap critically depends on the atomic-scale morphology of the interface: unlike the abrupt case, disordered interfaces exhibit localized states extending over the whole interface Brillouin zone. The presence of interfacial density of states, experimentally detectable, is therefore an indication of disorder and atomic interdiffusion
DIFFERENT SUN EXPOSURE HABITS BASED ON SEX, AGE, PHOTOTYPE AND EDUCATION
No full textAim. We analysed sun exposure attitudes and the knowledge of sun-related terminology in a group of persons living in Friuli Venezia Giulia with the aim to find out hazardous behaviours. On the basis of the results obtained we try to understand where and how to promote our educational efforts. Methods. An anonymous questionnaire consisting of 74 items was administered to 2 757 residents in Friuli Venezia Giulia concerning physical features, knowledge of terminology and sun-exposure attitudes. The data have been described for the whole sample and studied by logistic regression methods of analysis. Results. A very large proportion of interviewed people (80.1%) reported sunbathing, preferably in summer at the seaside. The statistical analysis of our data showed that 6.1% of our sample do sunbathing between 12 p.m. and 4 p.m., mainly young people aged 14-25 years, and that a high phototype and a low education level are a risk factor for sun-exposure more than 4 h daily. Sunscreens are more used by females (77%), by persons with high education levels (84%), low phototype and by persons who know the meaning of the term "melanoma" (86%). The purchase of sun protection products is rarely influenced by the dermatologist (6.5%), general practitioner (2.6%) or chemist (15.2%). The knowledge of commonly used sun-related terminology seems to be quite poor. Conclusion. This study shows that there is still a lot to do to awaken people to the importance of a correct sun exposure. Certainly, age and level of education influence sun exposure habits. The target of our intervention are young people and the dermatologist should partecipate actively at primary prevention.
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Pigmentatio maculosa eruptiva idiopathica: a case report and review of the literature.
No full textBACKGROUND: Pigmentatio maculosa eruptiva idiopathica is a rare pediatric disease characterized by asymptomatic, brownish macules involving the neck and trunk with no preceding inflammatory process or history of drug exposure.
METHODS: A 9-year-old girl presented with brown-gray, nonconfluent, asymptomatic macules on the trunk, neck, and limbs, ranging from 5 to 30 mm in diameter. The macules appeared suddenly with no lesions preceding their occurrence. Histopathologic examination showed basal cell layer hyperpigmentation, and abundant melanophages with a mild perivascular lymphohistiocytic infiltrate in the papillary dermis.
RESULTS: The lesions disappeared spontaneously 1.5 years later with no therapy. No relapse occurred.
CONCLUSION: Pigmentatio maculosa eruptiva idiopathica must be differentiated from other skin disorders with hyperpigmentation in pediatric practice in order to avoid unnecessary treatment, as spontaneous resolution is expected. Following a literature review, we underline the importance of spontaneous regression as an additional clinical feature for this disease
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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